Polymethoxyflavones in peel of Citrus reticulata ‘Chachi’ and their biological activities

Citrus polymethoxyflavones (PMFs) have been of increasing interest due to their extensive biological activities. In the present study, a total of eight PMFs were isolated from the peel of Citrus reticulata ‘Chachi’ (CRC). They were individually identified as 5-hydroxy-6,7,8,4′-tetramethoxyflavone (1), 5,6,7,3′,4′-pentamethoxyflavanone (2), 5-hydroxy-6,7,8,3′,4′-pentamethoxyflavone (3), 3,5,6,7,8,3′,4′- heptamethoxyflavone (4), 5,6,7,8,3′,4′-hexamethoxyflavone (5), 5,6,7,8,4′-pentamethoxyflavone (6), 6,7,8,3′,4′-pentamethoxyflavanone (7) and 5,6,7,3′,4′-pentamethoxyflavone (8) by nuclear magnetic resonance and mass spectroscopic analysis. 6,7,8,3′,4′-Pentamethoxyflavanone was isolated from the peel of CRC for the first time. The content of PMFs was firstly quantified in both the peel of CRC and PMF-rich extract by HPLC analysis. Furthermore, the biological activities of PMF compounds were investigated. 3,5,6,7,8,3′,4′-Heptamethoxyflavone demonstrated potent sterol regulatory element-binding proteins inhibition activity and 5-hydroxy-6,7,8,3′,4′-pentamethoxyflavone exhibited strong antiproliferative activity against tumor cell lines. The isolated PMF compounds could also significantly inhibit NO production and the effect varied mainly depending on the number of methoxy groups.